The present invention relates to a photometry device applicable to an SLR (Single Lens Reflex) camera, and more particularly to a photometry device with which exposure errors due to a difference of reflectivity of objects having different colors can be compensated.
Recently, in most cameras, reflection type photometry devices are employed. The reflection type photometry device receives the light, which is reflected by an object and passed through an observing optical system of a camera, using a light receiving element, determines the brightness of the object based on the output of the measured value, and then calculates the exposure value of the camera based on the measured brightness. However, this type of photometry device cannot detect the color of the object because of its structure. Accordingly, in such a device, the reflectivity of an object is generally assumed to be 18% and the exposure parameter is determined on this assumption. Therefore, regarding a whitish object whose reflectivity is greater than 18%, the determined brightness is greater than the actual brightness. If the camera controls an exposure operation based on the determined exposure value, the object is under exposed. Regarding a dark object whose reflectivity is less than 18%, such an object is over exposed in order to increase an exposure value. The difference of the reflectivity of the object may also occur depending on the color of the object. For example, when the color of an object is yellow, the reflectivity may be up to 70%. In such a case, if the standard reflectivity is assumed to be 18%, the exposure value is approximately 2 Ev lower than necessary. If the object color is blue, the reflectivity is approximately 9%. In this case, the object is over exposed by approximately 1 Ev greater than necessary.
Therefore, in the conventional photometry device, the photographer is required to guess the reflectivity of the object. Then, based on the reflectivity determined by the photographer, the exposure is controlled such that, if the object is a whitish or yellowish one having a relatively high reflectivity, it is to be overexposed, and if the object is a blackish or bluish one having a relatively low reflectivity, it is to be underexposed. With this operation, the above-described defects may be solved. However, to accurately guess the reflectivity of the object and control the exposure can be done only by experienced and skilled photographers. It is impossible to have all the photographers do such an operation. Further, it is not preferable that a manual operation of the photographer is required for exposure. Further, if such a manual operation is required, the camera becomes unsuitable, as the recent trend is for automatic photographing.
Recently, there is suggested a camera provided with a photometry device which divides the light from object into three-primary color components, and determines the color of the object based on the photometry outputs of respective color components. Since the color of the object is automatically determined, the above-described photographer""s operation becomes unnecessary. However, depending on the color purity of the object, the determined compensation value may not precisely correspond to the actual color of the object. For example, given that the object color is blue, the blue purity could fall in various conditions. That is, the blue purity of the object may be relatively high, or the purity may be relatively low and the light from the object may include red and/or green components as well. Since the blue purity could have various levels even if the object color is determined to be blue, it is not reliable if the compensation value corresponding to pure blue is determined to be the compensation value for such an object. That is, if the compensation value corresponding to pure blue object is used for the object whose blue purity is relatively low, the compensation value may cause over-exposed condition. On the contrary, if the compensation value is determined based on an object having relatively low blue purity, the pure blue object may be under-exposed.
Furthermore, when the above-described compensation is applied, inappropriate compensation values may also be obtained depending on the contrast of the object. That is, a bright portion of the object having a higher contrast has more influence on the compensation value than a bright portion of an object having a lower contrast. For example, when a portion of the object has a relatively high reflectivity and another portion has a relatively low reflectivity, if the exposure compensation is applied based on the portion having the low reflectivity, the portion having the high reflectivity may be over-exposed. In such a case, it is difficult to determine an appropriate exposure for an entire object.
It is therefore an object of the invention to provide an improved photometry device with which appropriate exposure values can be obtained regardless of difference of reflectivity, color purity and contrast of focused objects.
According to an aspect of the invention, there is provided a photometry device for a camera, which includes a normal light sensor having spectral sensitivity characteristics close to visual sensitivity characteristics, a plurality of colorimetric sensors having spectral sensitivity characteristics that are different from each other, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a colorimetry system that judges a color of the object in accordance with the outputs of the plurality of colorimetric sensors, and a compensation amount determining system that determines an exposure compensation amount in accordance with the color judged by the colorimetry system. The compensation amount determining system compensates for the exposure compensation amount determined by the compensation amount determining system in accordance with differences among the outputs of the plurality of colorimetric sensors.
With this configuration, appropriate exposure values can be obtained regardless of the difference of the reflectivity and color purity of objects.
Optionally, the compensation amount determining system may compensate for the exposure compensation amount such that the exposure compensation amount is made greater when the differences are greater.
In a particular case, the normal light sensor may include a normal light photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from approximately 500 nm through 600 nm, and the plurality of colorimetric sensors may include a blue light photometry sensor for metering blue light component, a green light photometry sensor for metering green light component, and a red light photometry sensor for metering red light component.
Further optionally, the compensation amount determining system calculates a difference between an output of one of the plurality of colorimetric sensors, and an average of outputs of the other of the plurality of colorimetric sensors, and the compensation amount determining system compensates the exposure compensation amount in accordance with the difference.
In the above case, the compensation amount determining system may compensate for the exposure compensation amount such that the larger the difference is, the greater the exposure compensation amount is.
Still optionally, each of the plurality of colorimetric sensors may have a light metering surface divided into a plurality of photometry areas, and the compensation amount determining system may determine the exposure compensation amount in accordance with the outputs at least one of the plurality of photometry areas.
In the above case, at least one of the plurality of photometry areas may include a center of an object subjected to be metered.
Alternatively, at least one of the plurality of photometry areas may overlap an area subjected to a distance measuring.
Optionally, the green light sensor is used as both the normal light sensor and the colorimetric sensor.
Further optionally, the normal light sensor may have a light metering surface divided into a plurality of photometry areas, the compensation amount determining system obtains a difference between a maximum output and a minimum output outputted from the plurality of photometry areas of the normal light sensor as a contrast value, the exposure compensation amount being compensated in accordance with the contrast value.
In the above case, compensation amount determining system may compensate for the exposure compensation amount such that the larger the contrast value is, the smaller the exposure compensation amount is.
According to another aspect of the invention, there is provided a photometry device for a camera, which is provided with a photometry system that divides a photographing area into a plurality of photometry areas and performs a photometry operation with respect to each of the plurality of photometry areas, a colorimetry system that performs a colorimetry operation with respect to at least one of the plurality of photometry areas, an exposure amount determining system that determines an exposure amount of an object in accordance with outputs of the photometry system, a compensation amount determining system that judges a color of the object in accordance with the output of the colorimetry system and determining an exposure compensation amount in accordance with the judged color, and an exposure compensation amount compensating system that compensates for the exposure compensation amount in accordance with the judged color and a difference between an output of the photometry system corresponding to the at least one of the photometry areas for which the colorimetry operation is performed and outputs of the photometry system corresponding to photometry areas adjacent to or surrounding at least one of the photometry areas.
Optionally, the at least one of the plurality of photometry areas may include a photometry area corresponding to a center of the photographing area.
Further, at least one of the plurality of photometry areas includes a point subjected to a distance measuring for focusing.
Still optionally, the exposure compensation amount compensating system may lower the exposure compensation amount if the judged color is a color having a high reflectivity, and if the output of the photometry system with respect to the photometry areas adjacent to or surrounding the at least one photometry area is low relative to the output of the photometry system with respect to the at least one photometry area. In a particular case, the exposure compensation amount is set to zero.
Optionally or alternatively, the exposure compensation amount compensating system may lower the exposure compensation amount if the judged color is a color having a low reflectivity, and if the output of the photometry system with respect to the photometry areas adjacent to or surrounding the at least one photometry area is high relative to the output of the photometry system with respect to the at least one photometry area. In a particular case, the exposure compensation amount is set to zero.
Alternatively, the exposure compensation amount may be set to zero by the exposure compensation amount compensating system if the judged color is red, and if a difference between the output of the photometry system with respect to the photometry areas adjacent to or surrounding the at least one photometry area, and the output of the photometry system with respect to the at least one photometry area is greater than a first predetermined value.
In this case, the exposure compensation amount is set to zero by the exposure compensation amount compensating system if the judged color is blue, and if the difference between the output of the photometry system with respect to the photometry areas adjacent to or surrounding the at least one photometry area, and the output of the photometry system with respect to the at least one photometry area is greater than a second predetermined value which is greater than the first predetermined value.
Further, the exposure compensation amount is set to zero by the exposure compensation amount compensating system if the judged color is yellow, and if the difference between the output of the photometry system with respect to the photometry areas adjacent to or surrounding the at least one photometry area, and the output of the photometry system with respect to the at least one photometry area is smaller than a third predetermined value which is smaller than the first predetermined value.
Still optionally, the photometry system may include a normal photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from 500 nm through 600 nm, and the colorimetry system may include a blue light photometry sensor for metering blue light component, a green light photometry sensor for metering green light component, and a red light photometry sensor for metering red light component.
In this case, the green light photometry sensor may be used as both the normal photometry sensor and the colorimetric sensor.
According to another aspect of the invention, there is provided a photometry device for a camera, which is provided with a photometry system that divides a photographing area into a plurality of photometry areas and performs a photometry operation with respect to each of the plurality of photometry areas, a colorimetry system that divides a photographing area into a plurality of areas and performs a colorimetry operation with respect to at least one of the plurality of areas, an exposure amount determining system that determines an exposure amount of an object in accordance with outputs of the photometry system, a compensation amount determining system that judges a color of the object in accordance with the output of the colorimetry system and determining an exposure compensation amount in accordance with the judged color, and an exposure compensation amount compensating system that compensates for the exposure compensation amount in accordance with differences among outputs of the photometry system.
Optionally, the compensation amount compensating system may compensate for the exposure compensation amount in accordance with a contrast value, the contrast value being defined as a difference between a maximum output and minimum output of the photometry system.
Optionally or alternatively, the compensation amount compensating system may compensate for the exposure compensation amount such that the greater the differences are, the smaller the exposure compensation amount is.
Further optionally or alternatively, the compensation amount compensating system may compensate for the exposure compensation amount such that the greater the contrast value is, the smaller the exposure compensation amount is.
Still optionally, the photometry system may include a normal photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from 500 nm through 600 nm, and the colorimetry system may include a blue light photometry sensor for metering blue light component, a green light photometry sensor for metering green light component, and a red light photometry sensor for metering red light component.
In this case, the green light photometry sensor may be used as both the normal photometry sensor and the colorimetric sensor.